A Canadian-led international clinical trial has found that post-menopausal survivors of early-stage breast cancer who took the drug letrozole after completing an initial five years of tamoxifen therapy had a significantly reduced risk of cancer recurrence compared to women taking a placebo. The results of the study appear in the on-line edition of the New England Journal of Medicine.

The clinical trial has been halted early because of the positive results and researchers are notifying the 5,187 women worldwide who have participated in the study. Women on letrozole will continue taking the drug and those on the placebo can begin taking letrozole, if they wish.

Study researchers found that letrozole, when taken after five years of tamoxifen therapy, substantially increased the chance of remaining cancer free. In total, 132 women taking the placebo had their disease recur compared to 75 on letrozole. Overall, letrozole reduced the risk of recurrence by 43 percent, so that after four years of participating in the trial, 13 percent of the women on the placebo, but only seven percent, of those on letrozole had recurred. Deaths from breast cancer were also reduced. Seventeen women taking the placebo died of breast cancer compared to nine taking letrozole.

While tamoxifen is widely used to prevent breast cancer recurrence in post-menopausal women, it stops being effective after five years because, scientists believe, tumours become resistant to it.

For more information on the results of this clinical trial and what it might mean for you: